Model R is the first of the IMF "Reference Series" loudspeakers. These differ slightly from the famous IMF "Monitoring Series" loudspeakers.Drivers reference : tweeter : KEF T27; medium : KEF B110, bass: KEF B139.
From a message posted on Yahoo :
The original model R (which was really the beginning of the Fried company) was a KEF Concerto kit(KEF B139, B110, T27 and KEF Xover) in a Bud Fried designed line tunnel (related to Dynaco A25 loading) with a tube (closed line) behind the midrange. The R2 replaced the KEF Xover with one designed specially for the R (interestingly it was also done by KEF). The R2 was a significant improvement over the original R.
Model R is the first of the IMF "Reference Series" loudspeakers. These differ slightly from the famous IMF "Monitoring Series" loudspeakers.
These loudspeakers incorporate the fundamental operating principles of the "Monitoring Series" and new features made possible by new technology and materials. Model R, for instance, can be used with less than the very best pickup arms and cartridges, and can deliver more dynamic range than has heretofore been possible from a moderately sized wide range loudspeakers.
Model R is instantly recognizables as an "IMF", with the famous "IMF sound", resulting from long time dedication to "monitoring" principles. IMF loudspeakers are known to be different in concept and execution from the usual "commercial" or "home" loudspeaker, and we might review these essential differences.
First, the drive system: Model R is a three way drive system, each driver specifically and chemically formulated for its operating range (see Illustration 1). A long time ago, the BBC and IMF dispensed with paper cone loudspeakers, which were found to be not suitable where accuracy was the requirement. Rather, plastic laminate drives were adopted for use in all frequency ranges, since they are superior in essential way, to wit:
Plastic cones are to paper cone as a sophisticated independent suspension is to a "wagon axle"; you use the latter only if you wish to "save money" at the expense of performances
Second, the enclosure: Model R has two totally separate systems, a transmission line for the mid range, and a resistive line tunnel for the bass range (Illustration 2). The mid line is identical to that used in previous IMF loudspeakers, a long tube with graded foam absorbents which absorb the sound from the back of the drive and ensure absolute purity of sound in the vital mid range. The line is, with its driver, the reason for the "open", "clear", and phase proper mid reproduction typical of IMF. By comparison, any closed back mid system, be it cone or dome, sound "as if you are speaking into a bucket"!
The resistive line tunnel for the bass is an IMF development. Driven by a flat piston woofer, whose geometric propagating point is several inches in front of the mid propagator (for minimal "time delay" effects on or off axis), it has several features for optimizing transient performance. Inside and behind the woofer are hanging edge-on absorbent filters (see Illustration 2), which provide maximum damping and minimum restriction. As in other IMF designs, this treatment is specifically to avoid "fast" reflections, which inevitably produce "box-y" upper bass. The tunnel at bottom is resistively foam damped and adjusted for optimum rise time consonant with subsonic stability. By comparison, sealed, stuffed boxes are primitive in design and sound that way. Modern research has shown why - they cannot have the transient properties of phase worthy system such as IMF "R" speakers.
All constricted bass systems sound "boxy", lack detail, and test poorly on transient inputs, such as the modern "impulse" development techniques used by IMF. Indeed, the "heavy", "mushy", "bass-ey" coloration typical of other loudspeakers is a distortion now called, by the experts, "transient intermodulation". Compared to that, IMF bass reproduction has timbre and "life", so that bass is not a dull thus, but the sound of a real instrument.
Woofer, mid and tweeter are joined by a phase compensated crossover system. They operate as homogeneous whole, like the ideal single cone loudspeaker of the text writers; and without the woofer-tweeter and other coloration so evident in most multi-way systems.
Model R features a new single control known as the "Impulse-Perspective" control. A toggle switch has "Plus", "Neutral" and "Minus" positions. "Neutral" is for most program material which is well recorded. "Plus", slightly increasing the rise time of the system is only for master tapes or other blemish free material (such as imported disc). "Minus" is for slightly distorted material; in this position, the speaker is made slightly less revealing, rounding off the rough edges of the program.
Model R has all the time proven IMF features, which we will briefly describe here. Like all IMFs, Model R is designed to be used free standing, the traditional "monitoring" position, away from walls, corners or floors; and thus less subject to involvement with the sound of the listening room.
Model R is built in mirror image pairs; a left and a right speaker, mid and tweeter at the inner edge of each, minimizing diffraction problems, bending the sound image inward and away from sound distorting walls; the famous "inward dispersion" system of IMF, and the major reason why IMF speakers are noted for a startlingly accurate stereo image.
In short, only a company like IMF, with long experience in monitoring techniques and quality, only a company employing the most advanced technologies, could produce Model R. It is not a " miracle" speaker, not a half developed "this year's model", but the end result of research and know how, employing new drive systems and techniques for an even better performance.
Model R will play safely at higher levels than previous IMFs. Model R can reproduce peak levels above those of the concert hall. For Model R is a breakthrough, a high accuracy loudspeaker of moderate size that is also wide range and plays loud. It is more than that: it is a linear transduceer, even on transients, so that it can reproduce the full dynamics and percussives of the fine program material just becoming available on discs. Model R, with piston action, linear drivers and transient proper enclosure, can project program into the room at higher levels without "screech", "boom" or "mud"!
Listeners tend to set program levels realistically, letting the dynamic peaks provide the musical excitement. They need not set an artificially high level "to get the music out of the box". as with conventional, non-linear "paper cone in a box" speakers!
Next to its exciting dynamic capability, the most striking virtue of Model R is its reproduction of the original timbres of voice and instruments. Listeners need not wonder whether it is an oboe or a clarinet, a tuba or a trombone, an organ pedal or a muffled drum roll, a bass guitar or a tympani. Sad to say, on most speakers, you just can't tell! (Try it!). This quality of Model R, known as "resolution", is a function of its time proper grouping of the fundamentals and harmonics of musical instruments; it is a result of its "impulse" development; and is something impossible to do with more conventional approaches. In addition, "resolution" recreates the source size and spatial position of the performers. Voice has its size and place, as do pianos and violins, no twenty foot wide piano keyboardds, no swaying choruses or other "source wander" effects on Model R.
Voice reproduction is superb, matched by only our own MONITOR in its realism. You can hear the breath formation, the throat control of the singer; just as in the original performance.
Rapid percussive intruments, such as guitar, harpsichord, piano, catanet, tympani, and bongo drum are superbly delineated in space. Piano, which is so difficult on other loudspeakers, is neutral and unforced.
Low frequency instruments, such as double bass, tuba, and organ, are also exciting (these have always been revered on IMF loudspeakers); instead of a whoosh, you feel the fundamental and hear the harmonics that give breath and life to them.
Frankly, people conditioned to "loudspeaker sound", rather than the sound of live instruments, do not like Model R at first hearing. They say it is "too clear", "too bright", or "lacks warmth". These are just ways of saying they are accustomed to "time smear" distortion. As in the past, whenever we have introduced more accurate loudspeakers, we respond to the same criticisms, and suggest they compare to live instruments, rather than to the sound of antiquated loudspeakers.
Model R is perhaps the most revealing loudspeaker ever produced by IMF, famous for furnishing the world's most accurate loudspeakers. Every program inputs sounds different, and sometimes you can even hear the differences in tape quality from one record band to another. Model R does all this with any stable, reliable amplifier of moderate power, sixty watts or less. It does not require involving oneself in the costs and problems of super amplifiers. Model R is a safe loudspeaker to use; its inbuilt fusing system permits high peak outputs while protecting against thermal overdrive, "accident", or amplifier failure.
Model R is an exciting new loudspeaker, based on the world famous IMF MONITORs. It is recommended wherever the user requires the most advanced standards of accuracy that the art of music reproduction can meet.
Drive complement:
KEF B139 SP1044, 8" x 12" flat piston woofer, visco elastic damped Bextrene
KEF B110 SP1003, 5" laminated plastic mid
KEF T27 SP1032, melinex dome tweeter
Impulse and frequency response:
Adjusted for optimum balance; frequency response, substantially flat 25Hz - 30 KHz
Impulse response adjustable by "Impulse-Perspective" Control
Crossovers: 375Hz, 3.5KHz, phase compensated and impulse damped
Efficiency: 25W. for 100db SPL (3 ft. on axis, noise, anechoic)
Impedance: 8 ohms
Supplied in matched, mirror image pairs only
Size: 28" high, 16" wide, 14 3/4" deep
Weight: 66 pounds
